System and method for utilizing sparse data containers in a striped volume set

ABSTRACT

A storage system architecture comprises one or more volumes distributed across the plurality of nodes interconnected as a cluster. The volumes are organized as a striped volume set (SVS) and configured to store content of data containers served by the cluster in response to data access requests issued by clients. The content of each data container is apportioned among the volumes of the SVS to thereby improve efficiency and storage service provided by the cluster. Each data container is implemented on each of the volumes of the SVS as a sparse data container which stores data amongst sections of sparseness within the data container.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a continuation-in-part of U.S. patentapplication Ser. No. 11/119,278, which was filed on Apr. 29, 2005, byMichael Kazar, et al. and entitled STORAGE SYSTEM ARCHITECTURE FORSTRIPING DATA CONTAINER CONTENT ACROSS VOLUMES OF A CLUSTER, publishedas U.S. patent application Publication No. 2005/0192932 on Sep. 1, 2005and is hereby incorporated by reference.

FIELD OF THE INVENTION

The present invention is directed to storage systems and, in particularto using sparse data containers to stripe data containers across aplurality of volumes on one or more storage systems.

BACKGROUND OF THE INVENTION

A storage system typically comprises one or more storage devices intowhich information may be entered, and from which information may beobtained, as desired. The storage system includes a storage operatingsystem that functionally organizes the system by, inter alia, invokingstorage operations in support of a storage service implemented by thesystem. The storage system may be implemented in accordance with avariety of storage architectures including, but not limited to, anetwork-attached storage environment, a storage area network and a diskassembly directly attached to a client or host computer. The storagedevices are typically disk drives organized as a disk array, wherein theterm “disk” commonly describes a self-contained rotating magnetic mediastorage device. The term disk in this context is synonymous with harddisk drive (HDD) or direct access storage device (DASD).

The storage operating system of the storage system may implement ahigh-level module, such as a file system, to logically organize theinformation stored on volumes as a hierarchical structure of datacontainers, such as files and logical units. For example, each “on-disk”file may be implemented as set of data structures, i.e., disk blocks,configured to store information, such as the actual data for the file.These data blocks are organized within a volume block number (vbn) spacethat is maintained by the file system. The file system may also assigneach data block in the file a corresponding “file offset” or file blocknumber (fbn). The file system typically assigns sequences of fbns on aper-file basis, whereas vbns are assigned over a larger volume addressspace. The file system organizes the data blocks within the vbn space asa “logical volume”; each logical volume may be, although is notnecessarily, associated with its own file system.

A known type of file system is a write-anywhere file system that doesnot overwrite data on disks. If a data block is retrieved (read) fromdisk into a memory of the storage system and “dirtied” (i.e., updated ormodified) with new data, the data block is thereafter stored (written)to a new location on disk to optimize write performance. Awrite-anywhere file system may initially assume an optimal layout suchthat the data is substantially contiguously arranged on disks. Theoptimal disk layout results in efficient access operations, particularlyfor sequential read operations, directed to the disks. An example of awrite-anywhere file system that is configured to operate on a storagesystem is the Write Anywhere File Layout (WAFL®) file system availablefrom Network Appliance, Inc., Sunnyvale, Calif.

The storage system may be further configured to operate according to aclient/server model of information delivery to thereby allow manyclients to access data containers stored on the system. In this model,the client may comprise an application, such as a database application,executing on a computer that “connects” to the storage system over acomputer network, such as a point-to-point link, shared local areanetwork (LAN), wide area network (WAN), or virtual private network (VPN)implemented over a public network such as the Internet. Each client mayrequest the services of the storage system by issuing file-based andblock-based protocol messages (in the form of packets) to the systemover the network.

A plurality of storage systems may be interconnected to provide astorage system environment configured to service many clients. Eachstorage system may be configured to service one or more volumes, whereineach volume stores one or more data containers. Yet often a large numberof data access requests issued by the clients may be directed to a smallnumber of data containers serviced by a particular storage system of theenvironment. A solution to such a problem is to distribute the volumesserviced by the particular storage system among all of the storagesystems of the environment. This, in turn, distributes the data accessrequests, along with the processing resources needed to service suchrequests, among all of the storage systems, thereby reducing theindividual processing load on each storage system. However, a noteddisadvantage arises when only a single data container, such as a file,is heavily accessed by clients of the storage system environment. As aresult, the storage system attempting to service the requests directedto that data container may exceed its processing resources and becomeoverburdened, with a concomitant degradation of speed and performance.

One technique for overcoming the disadvantages of having a single datacontainer that is heavily utilized is to stripe the data containeracross a plurality of volumes configured as a striped volume set (SVS),where each volume is serviced by a different storage system, therebydistributing the load for the single data container among a plurality ofstorage systems. In a striped file system utilizing a SVS, aconventional technique for striping data across the constituent volumesis to utilize dense data containers, i.e., data is stored from offsetzero through the end of the data container with no regions of the datacontainer that lack storage. In such a dense data container, the firststripe of data in a first volume of the SVS is stored at offset zerowithin the data container. Assuming that the data container issufficiently large so as to “wrap around” all of the volumes in the SVS,the next stripe of data that is stored on the same first volume isstored at an offset equal to the size of each stripe.

For example, assume a SVS contains data striped across three volumeswith the stripe size equal to 1 MB. A 5 MB dense data container, such asa file, is stored on the SVS with a first stripe at offset zero of afirst volume, a second stripe at offset zero of a second volume and athird stripe at offset zero of a third volume. Similarly, a fourthstripe is stored at offset 1 MB on the first volume and a final stripeis stored at offset 1 MB of the second volume. In order to efficientlyaccess a particular stripe of data, the file system must be able toquickly calculate the appropriate offset based upon striping rules andstripe size. While this offset calculation typically may be made inconstant time, the constant time may be significant if a complexstriping algorithm is utilized, thereby increasing the latency inserving data. Furthermore, in such a dense file, there exists apossibility that the metadata identifying the striping algorithm and/orstripe size may be damaged and/or corrupted. In such a situation,determining the order of stripes of data within the SVS may beimpossible, thereby resulting in data loss.

Additionally, should the data within the SVS need to be re-striped dueto, for example, the addition of a volume to the SVS, the calculationsrequired to safely re-stripe a densely stored file may be substantial.Such a re-striping operation may require relocation of significantportions of the data, which may consume a considerable amount of time.Re-striping may also require multiple copy operations to relocate eachstripe to the proper location, which increases the time required toperform the re-striping operation.

SUMMARY OF THE INVENTION

The present invention overcomes the disadvantages of the prior art byproviding a storage system architecture comprising one or more volumesdistributed across a plurality of nodes interconnected as a cluster. Thevolumes are organized as a striped volume set (SVS) and configured tostore content of data containers, such as files and logical units,served by the cluster in response to multi-protocol data access requestsissued by clients. Each node of the cluster includes (i) a storageserver adapted to service a volume of the SVS and (ii) a multi-protocolengine adapted to redirect the data access requests to any storageserver of the cluster. Notably, the content of each data container isapportioned among the volumes of the SVS to thereby improve theefficiency of storage service provided by the cluster.

In the illustrative embodiment, the SVS is associated with a set ofstriping rules that define a stripe algorithm, a stripe width and anordered list of volumes within the SVS. The stripe algorithm specifiesthe manner in which data container content is apportioned as stripesacross the plurality of volumes, while the stripe width specifies thesize/width of each stripe. Moreover, the ordered list of volumes mayspecify the function and implementation of the various volumes andstriping rules of the SVS. For example, the ordering of volumes in thelist may denote the manner of implementing a particular stripingalgorithm, e.g., round-robin.

According to an aspect of the invention, each data container storedwithin a SVS is implemented as a sparse data container. Each datacontainer stored within the SVS comprises one or more stripes of datastored on each constituent volume of the SVS in accordance with thestripe algorithm associated with the SVS. A region of each constituentvolume that is not currently storing a stripe of data is implemented asa sparse region with no assigned back-end storage. By utilizing regionsof sparseness, each data stripe of a data container within a SVS islocated at a predetermined offset. Illustratively, the predeterminedoffset is equal to the stripe number minus 1 multiplied by the stripesize, as the first stripe is located at offset zero, e.g., the fifthstripe of data begins at an offset four times the stripe width.

Advantageously, the use of sparse data containers facilitates processingof re-striping operations by moving a stripe of data from a currentlocation on a volume to an intended offset of an appropriate destinationvolume. The intended offset is thus sparse at the destination volume,thereby enabling easy re-striping operations. Additionally, if metadataassociated with the SVS is damaged to an extent that it is impossible toidentify the striping algorithm, the data container may be efficientlyreconstructed by examining each of the constituent volumes of the SVSand noting that the first stripe of data is located at offset zero, thesecond stripe of data located at an offset equal to the striped width,etc. Thus, the use of sparse data containers also improves dataavailability and protection.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and further advantages of invention may be better understoodby referring to the following description in conjunction with theaccompanying drawings in which like reference numerals indicateidentical or functionally similar elements:

FIG. 1 is a schematic block diagram of a plurality of nodesinterconnected as a cluster in accordance with an embodiment of thepresent invention;

FIG. 2 is a schematic block diagram of a node in accordance with anembodiment of the present invention;

FIG. 3 is a schematic block diagram of a storage operating system thatmay be advantageously used with the present invention;

FIG. 4 is a schematic block diagram illustrating the format of a clusterfabric (CF) message in accordance with an embodiment of with the presentinvention;

FIG. 5 is a schematic block diagram illustrating the format of a datacontainer handle in accordance with an embodiment of the presentinvention;

FIG. 6 is a schematic block diagram of an exemplary inode in accordancewith an embodiment of the present invention;

FIG. 7 is a schematic block diagram of an exemplary buffer tree inaccordance with an embodiment of the present invention;

FIG. 8 is a schematic block diagram of an illustrative embodiment of abuffer tree of a file that may be advantageously used with the presentinvention;

FIG. 9 is a schematic block diagram of an exemplary aggregate inaccordance with an embodiment of the present invention;

FIG. 10 is a schematic block diagram of an exemplary on-disk layout ofthe aggregate in accordance with an embodiment of the present invention;

FIG. 11 is a schematic block diagram illustrating a collection ofmanagement processes in accordance with an embodiment of the presentinvention;

FIG. 12 is a schematic block diagram of a volume location database(VLDB) volume entry in accordance with an embodiment of the presentinvention;

FIG. 13 is a schematic block diagram of a VLDB aggregate entry inaccordance with an embodiment of the present invention;

FIG. 14 is a schematic block diagram of a striped volume set (SVS) inaccordance with an embodiment of the present invention;

FIG. 15 is a schematic block diagram of a VLDB SVS entry in accordancewith an embodiment the present invention;

FIG. 16 is a schematic block diagram illustrating the periodicsparseness of file content stored on volumes of a SVS in accordance withan embodiment of the present invention;

FIG. 17 is a schematic block diagram of an exemplary file showingregions of sparseness in accordance with an embodiment of the presentinvention;

FIG. 18 is a schematic block diagram illustrating reconstruction of afile having periodic sparseness in accordance with an embodiment of thepresent invention; and

FIG. 19 is a flowchart detailing the steps of a procedure for creatingand using a striped volume set with sparse files in accordance with anembodiment of the present invention.

DETAILED DESCRIPTION OF AN ILLUSTRATIVE EMBODIMENT A. ClusterEnvironment

FIG. 1 is a schematic block diagram of a plurality of nodes 200interconnected as a cluster 100 and configured to provide storageservice relating to the organization of information on storage devices.The nodes 200 comprise various functional components that cooperate toprovide a distributed storage system architecture of the cluster 100. Tothat end, each node 200 is generally organized as a network element(N-module 310) and a disk element (D-module 350). The N-module 310includes functionality that enables the node 200 to connect to clients180 over a computer network 140, while each D-module 350 connects to oneor more storage devices, such as disks 130 of a disk array 120. Thenodes 200 are interconnected by a cluster switching fabric 150 which, inthe illustrative embodiment, may be embodied as a Gigabit Ethernetswitch. An exemplary distributed file system architecture is generallydescribed in U.S. Pat. No. 6,671,773 US 2002/0116593 titled METHOD ANDSYSTEM FOR RESPONDING TO FILE SYSTEM REQUESTS, by M. Kazar et al. issuedon Dec. 30, 2003. It should be noted that while there is shown an equalnumber of N and D-modules in the illustrative cluster 100, there may bediffering numbers of N and/or D-modules in accordance with variousembodiments of the present invention. For example, there may be aplurality of N-modules and/or D-modules interconnected in a clusterconfiguration 100 that does not reflect a one-to-one correspondencebetween the N and D-modules. As such, the description of a node 200comprising one N-module and one D-module should be taken as illustrativeonly.

The clients 180 may be general-purpose computers configured to interactwith the node 200 in accordance with a client/server model ofinformation delivery. That is, each client may request the services ofthe node, and the node may return the results of the services requestedby the client, by exchanging packets over the network 140. The clientmay issue packets including file-based access protocols, such as theCommon Internet File System (CIFS) protocol or Network File System (NFS)protocol, over the Transmission Control Protocol/Internet Protocol(TCP/IP) when accessing information in the form of files anddirectories. Alternatively, the client may issue packets includingblock-based access protocols, such as the Small Computer SystemsInterface (SCSI) protocol encapsulated over TCP (iSCSI) and SCSIencapsulated over Fibre Channel (FCP), when accessing information in theform of blocks.

B. Storage System Node

FIG. 2 is a schematic block diagram of a node 200 that is illustrativelyembodied as a storage system comprising a plurality of processors 222a,b, a memory 224, a network adapter 225, a cluster access adapter 226,a storage adapter 228 and local storage 230 interconnected by a systembus 223. The local storage 230 comprises one or more storage devices,such as disks, utilized by the node to locally store configurationinformation (e.g., in configuration table 235) provided by one or moremanagement processes that execute as user mode applications 1100 (seeFIG. 11). The cluster access adapter 226 comprises a plurality of portsadapted to couple the node 200 to other nodes of the cluster 100. In theillustrative embodiment, Ethernet is used as the clustering protocol andinterconnect media, although it will be apparent to those skilled in theart that other types of protocols and interconnects may be utilizedwithin the cluster architecture described herein. In alternateembodiments where the N-modules and D-modules are implemented onseparate storage systems or computers, the cluster access adapter 226 isutilized by the N/D-module for communicating with other N/D-modules inthe cluster 100.

Each node 200 is illustratively embodied as a dual processor storagesystem executing a storage operating system 300 that preferablyimplements a high-level module, such as a file system, to logicallyorganize the information as a hierarchical structure of nameddirectories, files and special types of files called virtual disks(hereinafter generally “blocks”) on the disks. However, it will beapparent to those of ordinary skill in the art that the node 200 mayalternatively comprise a single or more than two processor system.Illustratively, one processor 222 a executes the functions of theN-module 310 on the node, while the other processor 222 b executes thefunctions of the D-module 350.

The memory 224 illustratively comprises storage locations that areaddressable by the processors and adapters for storing software programcode and data structures associated with the present invention. Theprocessor and adapters may, in turn, comprise processing elements and/orlogic circuitry configured to execute the software code and manipulatethe data structures. The storage operating system 300, portions of whichis typically resident in memory and executed by the processing elements,functionally organizes the node 200 by, inter alia, invoking storageoperations in support of the storage service implemented by the node. Itwill be apparent to those skilled in the art that other processing andmemory means, including various computer readable media, may be used forstoring and executing program instructions pertaining to the inventiondescribed herein.

The network adapter 225 comprises a plurality of ports adapted to couplethe node 200 to one or more clients 180 over point-to-point links, widearea networks, virtual private networks implemented over a publicnetwork (Internet) or a shared local area network. The network adapter225 thus may comprise the mechanical, electrical and signaling circuitryneeded to connect the node to the network. Illustratively, the computernetwork 140 may be embodied as an Ethernet network or a Fibre Channel(FC) network. Each client 180 may communicate with the node over network140 by exchanging discrete frames or packets of data according topre-defined protocols, such as TCP/IP.

The storage adapter 228 cooperates with the storage operating system 300executing on the node 200 to access information requested by theclients. The information may be stored on any type of attached array ofwritable storage device media such as video tape, optical, DVD, magnetictape, bubble memory, electronic random access memory, micro-electromechanical and any other similar media adapted to store information,including data and parity information. However, as illustrativelydescribed herein, the information is preferably stored on the disks 130of array 120. The storage adapter comprises a plurality of ports havinginput/output (I/O) interface circuitry that couples to the disks over anI/O interconnect arrangement, such as a conventional high-performance,FC link topology.

Storage of information on each array 120 is preferably implemented asone or more storage “volumes” that comprise a collection of physicalstorage disks 130 cooperating to define an overall logical arrangementof volume block number (vbn) space on the volume(s). Each logical volumeis generally, although not necessarily, associated with its own filesystem. The disks within a logical volume/file system are typicallyorganized as one or more groups, wherein each group may be operated as aRedundant Array of Independent (or Inexpensive) Disks (RAID). Most RAIDimplementations, such as a RAID-4 level implementation, enhance thereliability/integrity of data storage through the redundant writing ofdata “stripes” across a given number of physical disks in the RAIDgroup, and the appropriate storing of parity information with respect tothe striped data. An illustrative example of a RAID implementation is aRAID-4 level implementation, although it should be understood that othertypes and levels of RAID implementations may be used in accordance withthe inventive principles described herein.

C. Storage Operating System

To facilitate access to the disks 130, the storage operating system 300implements a write-anywhere file system that cooperates with one or morevirtualization modules to “virtualize” the storage space provided bydisks 130. The file system logically organizes the information as ahierarchical structure of named directories and files on the disks. Each“on-disk” file may be implemented as set of disk blocks configured tostore information, such as data, whereas the directory may beimplemented as a specially formatted file in which names and links toother files and directories are stored. The virtualization module(s)allow the file system to further logically organize information as ahierarchical structure of blocks on the disks that are exported as namedlogical unit numbers (luns).

In the illustrative embodiment, the storage operating system ispreferably the NetApp® Data ONTAP® operating system available fromNetwork Appliance, Inc., Sunnyvale, Calif. that implements a WriteAnywhere File Layout (WAFL®) file system. However, it is expresslycontemplated that any appropriate storage operating system may beenhanced for use in accordance with the inventive principles describedherein. As such, where the term “ONTAP” is employed, it should be takenbroadly to refer to any storage operating system that is otherwiseadaptable to the teachings of this invention.

FIG. 3 is a schematic block diagram of the storage operating system 300that may be advantageously used with the present invention. The storageoperating system comprises a series of software layers organized to forman integrated network protocol stack or, more generally, amulti-protocol engine 325 that provides data paths for clients to accessinformation stored on the node using block and file access protocols.The multi-protocol engine includes a media access layer 312 of networkdrivers (e.g., gigabit Ethernet drivers) that interfaces to networkprotocol layers, such as the IP layer 314 and its supporting transportmechanisms, the TCP layer 316 and the User Datagram Protocol (UDP) layer315. A file system protocol layer provides multi-protocol file accessand, to that end, includes support for the Direct Access File System(DAFS) protocol 318, the NFS protocol 320, the CIFS protocol 322 and theHypertext Transfer Protocol (HTTP) protocol 324. A VI layer 326implements the VI architecture to provide direct access transport (DAT)capabilities, such as RDMA, as required by the DAFS protocol 318. AniSCSI driver layer 328 provides block protocol access over the TCP/IPnetwork protocol layers, while a FC driver layer 330 receives andtransmits block access requests and responses to and from the node. TheFC and iSCSI drivers provide FC-specific and iSCSI-specific accesscontrol to the blocks and, thus, manage exports of luns to either iSCSIor FCP or, alternatively, to both iSCSI and FCP when accessing theblocks on the node 200.

In addition, the storage operating system includes a series of softwarelayers organized to form a storage server 365 that provides data pathsfor accessing information stored on the disks 130 of the node 200. Tothat end, the storage server 365 includes a file system module 360 incooperating relation with a volume striping module (VSM) 370, a RAIDsystem module 380 and a disk driver system module 390. The RAID system380 manages the storage and retrieval of information to and from thevolumes/disks in accordance with I/O operations, while the disk driversystem 390 implements a disk access protocol such as, e.g., the SCSIprotocol. The VSM 370 illustratively implements a striped volume set(SVS) of the present invention. As described further herein, the VSMcooperates with the file system 360 to enable storage server 365 toservice a volume of the SVS. In particular, the VSM 370 implements aLocate( ) function 375 to compute the location of data container contentin the SVS volume to thereby ensure consistency of such content servedby the cluster.

The file system 360 implements a virtualization system of the storageoperating system 300 through the interaction with one or morevirtualization modules illustratively embodied as, e.g., a virtual disk(vdisk) module (not shown) and a SCSI target module 335. The vdiskmodule enables access by administrative interfaces, such as a userinterface of a management framework 1110 (see FIG. 11), in response to auser (system administrator) issuing commands to the node 200. The SCSItarget module 335 is generally disposed between the FC and iSCSI drivers328, 330 and the file system 360 to provide a translation layer of thevirtualization system between the block (lun) space and the file systemspace, where luns are represented as blocks.

The file system 360 is illustratively a message-based system thatprovides logical volume management capabilities for use in access to theinformation stored on the storage devices, such as disks. That is, inaddition to providing file system semantics, the file system 360provides functions normally associated with a volume manager. Thesefunctions include (i) aggregation of the disks, (ii) aggregation ofstorage bandwidth of the disks, and (iii) reliability guarantees, suchas mirroring and/or parity (RAID). The file system 360 illustrativelyimplements the WAFL file system (hereinafter generally the“write-anywhere file system”) having an on-disk format representationthat is block-based using, e.g., 4 kilobyte (KB) blocks and using indexnodes (“inodes”) to identify files and file attributes (such as creationtime, access permissions, size and block location). The file system usesfiles to store meta-data describing the layout of its file system; thesemeta-data files include, among others, an inode file. A file handle,i.e., an identifier is that includes an inode number, is used toretrieve an inode from disk.

Broadly stated, all inodes of the write-anywhere file system areorganized into the inode file. A file system (fs) info block specifiesthe layout of information in the file system and includes an inode of afile that includes all other inodes of the file system. Each logicalvolume (file system) has an fsinfo block that is preferably stored at afixed location within, e.g., a RAID group. The inode of the inode filemay directly reference (point to) data blocks of the inode file or mayreference indirect blocks of the inode file that, in turn, referencedata blocks of the inode file. Within each data block of the inode fileare embedded inodes, each of which may reference indirect blocks that,in turn, reference data blocks of a file.

Operationally, a request from the client 180 is forwarded as a packetover the computer network 140 and onto the node 200 where it is receivedat the network adapter 225. A network driver (of layer 312 or layer 330)processes the packet and, if appropriate, passes it on to a networkprotocol and file access layer for additional processing prior toforwarding to the write-anywhere file system 360. Here, the file systemgenerates operations to load (retrieve) the requested data from disk 130if it is not resident “in core”, i.e., in memory 224. If the informationis not in memory, the file system 360 indexes into the inode file usingthe inode number to access an appropriate entry and retrieve a logicalvbn. The file system then passes a message structure including thelogical vbn to the RAID system 380; the logical vbn is mapped to a diskidentifier and disk block number (disk,dbn) and sent to an appropriatedriver (e.g., SCSI) of the disk driver system 390. The disk driveraccesses the dbn from the specified disk 130 and loads the requesteddata block(s) in memory for processing by the node. Upon completion ofthe request, the node (and operating system) returns a reply to theclient 180 over the network 140.

It should be noted that the software “path” through the storageoperating system layers described above needed to perform data storageaccess for the client request received at the node may alternatively beimplemented in hardware. That is, in an alternate embodiment of theinvention, a storage access request data path may be implemented aslogic circuitry embodied within a field programmable gate array (FPGA)or an application specific integrated circuit (ASIC). This type ofhardware implementation increases the performance of the storage serviceprovided by node 200 in response to a request issued by client 180.Moreover, in another alternate embodiment of the invention, theprocessing elements of adapters 225, 228 may be configured to offloadsome or all of the packet processing and storage access operations,respectively, from processor 222, to thereby increase the performance ofthe storage service provided by the node. It is expressly contemplatedthat the various processes, architectures and procedures describedherein can be implemented in hardware, firmware or software.

As used herein, the term “storage operating system” generally refers tothe computer-executable code operable on a computer to perform a storagefunction that manages data access and may, in the case of a node 200,implement data access semantics of a general purpose operating system.The storage operating system can also be implemented as a microkernel,an application program operating over a general-purpose operatingsystem, such as UNIX® or Windows NT®, or as a general-purpose operatingsystem with configurable functionality, which is configured for storageapplications as described herein.

In addition, it will be understood to those skilled in the art that theinvention described herein may apply to any type of special-purpose(e.g., file server, filer or storage serving appliance) orgeneral-purpose computer, including a standalone computer or portionthereof, embodied as or including a storage system. Moreover, theteachings of this invention can be adapted to a variety of storagesystem architectures including, but not limited to, a network-attachedstorage environment, a storage area network and disk assemblydirectly-attached to a client or host computer. The term “storagesystem” should therefore be taken broadly to include such arrangementsin addition to any subsystems configured to perform a storage functionand associated with other equipment or systems. It should be noted thatwhile this description is written in terms of a write any where filesystem, the teachings of the present invention may be utilized with anysuitable file system, including a write in place file system.

D. CF Protocol

In the illustrative embodiment, the storage server 365 is embodied asD-module 350 of the storage operating system 300 to service one or morevolumes of array 120. In addition, the multi-protocol engine 325 isembodied as N-module 310 to (i) perform protocol termination withrespect to a client issuing incoming data access request packets overthe network 140, as well as (ii) redirect those data access requests toany storage server 365 of the cluster 100. Moreover, the N-module 310and D-module 350 cooperate to provide a highly-scalable, distributedstorage system architecture of the cluster 100. To that end, each moduleincludes a cluster fabric (CF) interface module 340 a,b adapted toimplement intra-cluster communication among the modules, includingD-module-to-D-module communication for data container stripingoperations described herein.

The protocol layers, e.g., the NFS/CIFS layers and the iSCSI/FC layers,of the N-module 310 function as protocol servers that translatefile-based and block based data access requests from clients into CFprotocol messages used for communication with the D-module 350. That is,the N-module servers convert the incoming data access requests into filesystem primitive operations (commands) that are embedded within CFmessages by the CF interface module 340 for transmission to theD-modules 350 of the cluster 100. Notably, the CF interface modules 340cooperate to provide a single file system image across all D-modules 350in the cluster 100. Thus, any network port of an N-module that receivesa client request can access any data container within the single filesystem image located on any D-module 350 of the cluster.

Further to the illustrative embodiment, the N-module 310 and D-module350 are implemented as separately-scheduled processes of storageoperating system 300; however, in an alternate embodiment, the modulesmay be implemented as pieces of code within a single operating systemprocess. Communication between an N-module and D-module is thusillustratively effected through the use of message passing between themodules although, in the case of remote communication between anN-module and D-module of different nodes, such message passing occursover the cluster switching fabric 150. A known message-passing mechanismprovided by the storage operating system to transfer information betweenmodules (processes) is the Inter Process Communication (IPC) mechanism.The protocol used with the IPC mechanism is illustratively a genericfile and/or block-based “agnostic” CF protocol that comprises acollection of methods/functions constituting a CF applicationprogramming interface (API). Examples of such an agnostic protocol arethe SpinFS and SpinNP protocols available from Network Appliance, Inc.The SpinFS protocol is described in the above-referenced U.S. Pat. No.6,671,773.

The CF interface module 340 implements the CF protocol for communicatingfile system commands among the modules of cluster 100. Communication isillustratively effected by the D-module exposing the CF API to which anN-module (or another D-module) issues calls. To that end, the CFinterface module 340 is organized as a CF encoder and CF decoder. The CFencoder of e.g., CF interface 340 a on N-module 310 encapsulates a CFmessage as (i) a local procedure call (LPC) when communicating a filesystem command to a D-module 350 residing on the same node 200 or (ii) aremote procedure call (RPC) when communicating the command to a D-moduleresiding on a remote node of the cluster 100. In either case, the CFdecoder of CF interface 340 b on D-module 350 de-encapsulates the CFmessage and processes the file system command.

FIG. 4 is a schematic block diagram illustrating the format of a CFmessage 400 in accordance with an embodiment of with the presentinvention. The CF message 400 is illustratively used for RPCcommunication over the switching fabric 150 between remote modules ofthe cluster 100; however, it should be understood that the term “CFmessage” may be used generally to refer to LPC and RPC communicationbetween modules of the cluster. The CF message 400 includes a mediaaccess layer 402, an IP layer 404, a UDP layer 406, a reliableconnection (RC) layer 408 and a CF protocol layer 410. As noted, the CFprotocol is a generic file system protocol that conveys file systemcommands related to operations contained within client requests toaccess data containers stored on the cluster 100; the CF protocol layer410 is that portion of message 400 that carries the file systemcommands. Illustratively, the CF protocol is datagram based and, assuch, involves transmission of messages or “envelopes” in a reliablemanner from a source (e.g., an N-module 310) to a destination (e.g., aD-module 350). The RC layer 408 implements a reliable transport protocolthat is adapted to process such envelopes in accordance with aconnectionless protocol, such as UDP 406.

A data container, e.g., a file, is accessed in the file system using adata container handle. FIG. 5 is a schematic block diagram illustratingthe format of a data container handle 500 including a SVS ID field 502,an inode number field 504, a unique-ifier field 506, a striped flagfield 508 and a striping epoch number field 510. The SVS ID field 502contains a global identifier (within the cluster 100) of the SVS withinwhich the data container resides. The inode number field 504 contains aninode number of an inode (within an inode file) pertaining to the datacontainer. The unique-ifier field 506 contains a monotonicallyincreasing number that uniquely identifies the data container handle500. The unique-ifier is particularly useful in the case where an inodenumber has been deleted, reused and reassigned to a new data container.The unique-ifier distinguishes that reused inode number in a particulardata container from a potentially previous use of those fields. Thestriped flag field 508 is illustratively a Boolean value that identifieswhether the data container is striped or not. The striping epoch numberfield 510 indicates the appropriate striping technique for use with thisdata container for embodiments where the SVS utilizes differing stripingtechniques for different data containers.

E. File System Organization

In the illustrative embodiment, a data container is represented in thewrite-anywhere file system as an inode data structure adapted forstorage on the disks 130. FIG. 6 is a schematic block diagram of aninode 600, which preferably includes a meta-data section 605 and a datasection 660. The information stored in the meta-data section 605 of eachinode 600 describes the data container (e.g., a file) and, as such,includes the type (e.g., regular, directory, vdisk) 610 of file, itssize 615, time stamps (e.g., access and/or modification time) 620 andownership, i.e., user identifier (UID 625) and group ID (GID 630), ofthe file. The meta-data section 605 also includes a generation number631, and a meta-data invalidation flag field 634. As described furtherherein, meta-data invalidation flag field 634 is used to indicatewhether meta-data in this inode is usable or whether it should bere-acquired from the MDV. The contents of the data section 660 of eachinode may be interpreted differently depending upon the type of file(inode) defined within the type field 610. For example, the data section660 of a directory inode contains meta-data controlled by the filesystem, whereas the data section of a regular inode contains file systemdata. In this latter case, the data section 660 includes arepresentation of the data associated with the file.

Specifically, the data section 660 of a regular on-disk inode mayinclude file system data or pointers, the latter referencing 4 KB datablocks on disk used to store the file system data. Each pointer ispreferably a logical vbn to facilitate efficiency among the file systemand the RAID system 380 when accessing the data on disks. Given therestricted size (e.g., 128 bytes) of the inode, file system data havinga size that is less than or equal to 64 bytes is represented, in itsentirety, within the data section of that inode. However, if the lengthof the contents of the data container exceeds 64 bytes but less than orequal to 64 KB, then the data section of the inode (e.g., a first levelinode) comprises up to 16 pointers, each of which references a 4 KBblock of data on the disk.

Moreover, if the size of the data is greater than 64 KB but less than orequal to 64 megabytes (MB), then each pointer in the data section 660 ofthe inode (e.g., a second level inode) references an indirect block(e.g., a first level L1 block) that contains 1024 pointers, each ofwhich references a 4 KB data block on disk. For file system data havinga size greater than 64 MB, each pointer in the data section 660 of theinode (e.g., a third level L3 inode) references a double-indirect block(e.g., a second level L2 block) that contains 1024 pointers, eachreferencing an indirect (e.g., a first level L1) block. The indirectblock, in turn, that contains 1024 pointers, each of which references a4 KB data block on disk. When accessing a file, each block of the filemay be loaded from disk 130 into the memory 224.

When an on-disk inode (or block) is loaded from disk 130 into memory224, its corresponding in-core structure embeds the on-disk structure.For example, the dotted line surrounding the inode 600 indicates thein-core representation of the on-disk inode structure. The in-corestructure is a block of memory that stores the on-disk structure plusadditional information needed to manage data in the memory (but not ondisk). The additional information may include, e.g., a “dirty” bit 670.After data in the inode (or block) is updated/modified as instructed by,e.g., a write operation, the modified data is marked “dirty” using thedirty bit 670 so that the inode (block) can be subsequently “flushed”(stored) to disk. The in-core and on-disk format structures of the WAFLfile system, including the inodes and inode file, are disclosed anddescribed in the previously incorporated U.S. Pat. No. 5,819,292 titledMETHOD FOR MAINTAINING CONSISTENT STATES OF A FILE SYSTEM AND FORCREATING USER-ACCESSIBLE READ-ONLY COPIES OF A FILE SYSTEM by David Hitzet al., issued on Oct. 6, 1998.

FIG. 7 is a schematic block diagram of an embodiment of a buffer tree ofa file that may be advantageously used with the present invention. Thebuffer tree is an internal representation of blocks for a file (e.g.,file 700) loaded into the memory 224 and maintained by thewrite-anywhere file system 360. A root (top-level) inode 702, such as anembedded inode, references indirect (e.g., level 1) blocks 704. Notethat there may be additional levels of indirect blocks (e.g., level 2,level 3) depending upon the size of the file. The indirect blocks (andinode) contain pointers 705 that ultimately reference data blocks 706used to store the actual data of the file. That is, the data of file 700are contained in data blocks and the locations of these blocks arestored in the indirect blocks of the file. Each level 1 indirect block704 may contain pointers to as many as 1024 data blocks. According tothe “write anywhere” nature of the file system, these blocks may belocated anywhere on the disks 130.

A file system layout is provided that apportions an underlying physicalvolume into one or more virtual volumes (or flexible volume) of astorage system, such as node 200. An example of such a file systemlayout is described in U.S. patent application Ser. No. 10/836,817titled EXTENSION OF WRITE ANYWHERE FILE SYSTEM LAYOUT, by John K.Edwards et al. and assigned to Network Appliance, Inc., now issued asU.S. Pat. No. 7,409,494 on Aug. 5, 2008. The underlying physical volumeis an aggregate comprising one or more groups of disks, such as RAIDgroups, of the node. The aggregate has its own physical volume blocknumber (pvbn) space and maintains meta-data, such as block allocationstructures, within that pvbn space. Each flexible volume has its ownvirtual volume block number (vvbn) space and maintains meta-data, suchas block allocation structures, within that vvbn space. Each flexiblevolume is a file system that is associated with a container file; thecontainer is file is a file in the aggregate that contains all blocksused by the flexible volume. Moreover, each flexible volume comprisesdata blocks and indirect blocks that contain block pointers that pointat either other indirect blocks or data blocks.

In one embodiment, pvbns are used as block pointers within buffer treesof files (such as file 700) stored in a flexible volume. This “hybrid”flexible volume embodiment involves the insertion of only the pvbn inthe parent indirect block (e.g., inode or indirect block). On a readpath of a logical volume, a “logical” volume (vol) info block has one ormore pointers that reference one or more fsinfo blocks, each of which,in turn, points to an inode file and its corresponding inode buffertree. The read path on a flexible volume is generally the same,following pvbns (instead of vvbns) to find appropriate locations ofblocks; in this context, the read path (and corresponding readperformance) of a flexible volume is substantially similar to that of aphysical volume. Translation from pvbn-to-disk,dbn occurs at the filesystem/RAID system boundary of the storage operating system 300.

In an illustrative dual vbn hybrid flexible volume embodiment, both apvbn and its corresponding vvbn are inserted in the parent indirectblocks in the buffer tree of a file. That is, the pvbn and vvbn arestored as a pair for each block pointer in most buffer tree structuresthat have pointers to other blocks, e.g., level 1 (L1) indirect blocks,inode file level 0 (L0) blocks. FIG. 8 is a schematic block diagram ofan illustrative embodiment of a buffer tree of a file 800 that may beadvantageously used with the present invention. A root (top-level) inode802, such as an embedded inode, references indirect (e.g., level 1)blocks 804. Note that there may be additional levels of indirect blocks(e.g., level 2, level 3) depending upon the size of the file. Theindirect blocks (and inode) contain pvbn/vvbn pointer pair structures808 that ultimately reference data blocks 806 used to store the actualdata of the file.

The pvbns reference locations on disks of the aggregate, whereas thevvbns reference locations within files of the flexible volume. The useof pvbns as block pointers 808 in the indirect blocks 804 providesefficiencies in the read paths, while the use of vbn block pointersprovides efficient access to required meta-data. That is, when freeing ablock of a file, the parent indirect block in the file contains readilyavailable vvbn block pointers, which avoids the latency associated withaccessing an owner map to perform pvbn-to-vvbn translations; yet, on theread path, the pvbn is available.

FIG. 9 is a schematic block diagram of an embodiment of an aggregate 900that may be advantageously used with the present invention. Luns(blocks) 902, directories 904, qtrees 906 and files 908 may be containedwithin flexible volumes 910, such as dual vbn flexible volumes, that, inturn, are contained within the aggregate 900. The aggregate 900 isillustratively layered on top of the RAID system, which is representedby at least one RAID plex 950 (depending upon whether the storageconfiguration is mirrored), wherein each plex 950 comprises at least oneRAID group 960. Each RAID group further comprises a plurality of disks930, e.g., one or more data (D) disks and at least one (P) parity disk.

Whereas the aggregate 900 is analogous to a physical volume of aconventional storage system, a flexible volume is analogous to a filewithin that physical volume. That is, the aggregate 900 may include oneor more files, wherein each file contains a flexible volume 910 andwherein the sum of the storage space consumed by the flexible volumes isphysically smaller than (or equal to) the size of the overall physicalvolume. The aggregate utilizes a physical pvbn space that defines astorage space of blocks provided by the disks of the physical volume,while each embedded flexible volume (within a file) utilizes a logicalwbn space to organize those blocks, e.g., as files. Each wbn space is anindependent set of numbers that corresponds to locations within thefile, which locations are then translated to dbns on disks. Since theflexible volume 910 is also a logical volume, it has its own blockallocation structures (e.g., active, space and summary maps) in its wbnspace.

A container file is a file in the aggregate that contains all blocksused by a flexible volume. The container file is an internal (to theaggregate) feature that supports a flexible volume; illustratively,there is one container file per flexible volume. Similar to a purelogical volume in a file approach, the container file is a hidden file(not accessible to a user) in the aggregate that holds every block inuse by the flexible volume. The aggregate includes an illustrativehidden meta-data root directory that contains subdirectories offlexible-volumes:

-   -   WAFL/fsid/filesystem file, storage label file

Specifically, a physical file system (WAFL) directory includes asubdirectory for each flexible volume in the aggregate, with the name ofsubdirectory being a file system identifier (fsid) of the flexiblevolume. Each fsid subdirectory (flexible volume) contains at least twofiles, a filesystem file and a storage label file. The storage labelfile is illustratively a 4 KB file that contains meta-data similar tothat stored in a conventional raid label. In other words, the storagelabel file is the analog of a raid label and, as such, containsinformation about the state of the flexible volume such as, e.g., thename of the flexible volume, a universal unique identifier (uuid) andfsid of the flexible volume, whether it is online, being created orbeing destroyed, etc.

FIG. 10 is a schematic block diagram of an on-disk representation of anaggregate 1000. The storage operating system 300, e.g., the RAID system380, assembles a physical volume of pvbns to create the aggregate 1000,with pvbns 1 and 2 comprising a “physical” volinfo block 1002 for theaggregate. The volinfo block 1002 contains block pointers to fsinfoblocks 1004, each of which may represent a snapshot of the aggregate.Each fsinfo block 1004 includes a block pointer to an inode file 1006that contains inodes of a plurality of files, including an owner map1010, an active map 1012, a summary map 1014 and a space map 1016, aswell as other special meta-data files. The inode file 1006 furtherincludes a root directory 1020 and a “hidden” meta-data root directory1030, the latter of which includes a namespace having files related to aflexible volume in which users cannot “see” the files. The hiddenmeta-data root directory includes the WAFL/fsid/directory structure thatcontains filesystem file 1040 and storage label file 1090. Note thatroot directory 1020 in the aggregate is empty; all files related to theaggregate are organized within the hidden meta-data root directory 1030.

In addition to being embodied as a container file having level 1 blocksorganized as a container map, the filesystem file 1040 includes blockpointers that reference various file systems embodied as flexiblevolumes 1050. The aggregate 1000 maintains these flexible volumes 1050at special reserved inode numbers. Each flexible volume 1050 also hasspecial reserved inode numbers within its flexible volume space that areused for, among other things, the block allocation bitmap structures. Asnoted, the block allocation bitmap structures, e.g., active map 1062,summary map 1064 and space map 1066, are located in each flexiblevolume.

Specifically, each flexible volume 1050 has the same inode filestructure/content as the aggregate, with the exception that there is noowner map and no WAFL/fsid/filesystem file, storage label file directorystructure in a hidden meta-data root directory 1080. To that end, eachflexible volume 1050 has a volinfo block 1052 that points to one or morefsinfo blocks 1054, each of which may represent a snapshot, along withthe active file system of the flexible volume. Each fsinfo block, inturn, points to an inode file 1060 that, as noted, has the same inodestructure/content as the aggregate with the exceptions noted above. Eachflexible volume 1050 has its own inode file 1060 and distinct inodespace with corresponding inode numbers, as well as its own root (fsid)directory 1070 and subdirectories of files that can be exportedseparately from other flexible volumes.

The storage label file 1090 contained within the hidden meta-data rootdirectory 1030 of the aggregate is a small file that functions as ananalog to a conventional raid label. A raid label includes physicalinformation about the storage system, such as the volume name; thatinformation is loaded into the storage label file 1090. Illustratively,the storage label file 1090 includes the name 1092 of the associatedflexible volume 1050, the online/offline status 1094 of the flexiblevolume, and other identity and state information 1096 of the associatedflexible volume (whether it is in the process of being created ordestroyed).

F. VLDB

FIG. 11 is a schematic block diagram illustrating a collection ofmanagement processes that execute as user mode applications 1100 on thestorage operating system 300 to provide management of configurationinformation (i.e. management data) for the nodes of the cluster. To thatend, the management processes include a management framework process1110 and a volume location database (VLDB) process 1130, each utilizinga data replication service (RDB 1150) linked as a library. Themanagement framework 1110 provides a user to an administrator 1170interface via a command line interface (CLI) and/or a web-basedgraphical user interface (GUI). The management framework isillustratively based on a conventional common interface model (CIM)object manager that provides the entity to which users/systemadministrators interact with a node 200 in order to manage the cluster100.

The VLDB 1130 is a database process that tracks the locations of variousstorage components (e.g., SVSs, flexible volumes, aggregates, etc.)within the cluster 100 to thereby facilitate routing of requeststhroughout the cluster. In the illustrative embodiment, the N-module 310of each node accesses a configuration table 235 that maps the SVS ID 502of a data container handle 500 to a D-module 350 that “owns” (services)the data container within the cluster. The VLDB includes a plurality ofentries which, in turn, provide the contents of entries in theconfiguration table 235; among other things, these VLDB entries keeptrack of the locations of the flexible volumes (hereinafter generally“volumes 910”) and aggregates 900 within the cluster. Examples of suchVLDB entries include a VLDB volume entry 1200 and a VLDB aggregate entry1300.

FIG. 12 is a schematic block diagram of an exemplary VLDB volume entry1200. The entry 1200 includes a volume ID field 1205, an aggregate IDfield 1210 and, in alternate embodiments, additional fields 1215. Thevolume ID field 1205 contains an ID that identifies a volume 910 used ina volume location process. The aggregate ID field 1210 identifies theaggregate 900 containing the volume identified by the volume ID field1205. Likewise, FIG. 13 is a schematic block diagram of an exemplaryVLDB aggregate entry 1300. The entry 1300 includes an aggregate ID field1305, a D-module ID field 1310 and, in alternate embodiments, additionalfields 1315. The aggregate ID field 1305 contains an ID of a particularaggregate 900 in the cluster 100. The D-module ID field 1310 contains anID of the D-module hosting the particular aggregate identified by theaggregate ID field 1305.

The VLDB illustratively implements a RPC interface, e.g., a Sun RPCinterface, which allows the N-module 310 to query the VLDB 1130. Whenencountering contents of a data container handle 500 that are not storedin its configuration table, the N-module sends an RPC to the VLDBprocess. In response, the VLDB 1130 returns to the N-module theappropriate mapping information, including an ID of the D-module thatowns the data container. The N-module caches the information in itsconfiguration table 235 and uses the D-module ID to forward the incomingrequest to the appropriate data container. All functions andinteractions between the N-module 310 and D-module 350 are coordinatedon a cluster-wide basis through the collection of management processesand the RDB library user mode applications 1100.

To that end, the management processes have interfaces to (are closelycoupled to) RDB 1150. The RDB comprises a library that provides apersistent object store (storing of objects) for the management dataprocessed by the management processes. Notably, the RDB 1150 replicatesand synchronizes the management data object store access across allnodes 200 of the cluster 100 to thereby ensure that the RDB databaseimage is identical on all of the nodes 200. At system startup, each node200 records the status/state of its interfaces and IP addresses (thoseIP addresses it “owns”) into the RDB database.

G. Storage System Architecture

In the illustrative embodiment of the present invention, the storagesystem architecture illustratively comprises two or more volumes 910distributed across a plurality of nodes 200 of cluster 100. The volumesare organized as a SVS and configured to store content of datacontainers, such as files and luns, served by the cluster in response tomulti-protocol data access requests issued by clients 180. Notably, thecontent of each data container is apportioned among the volumes of theSVS to thereby improve the efficiency of storage service provided by thecluster. To facilitate a description and understanding of the presentinvention, data containers are hereinafter referred to generally as“files”.

The SVS comprises a meta-data volume (MDV) and one or more data volumesis (DV). The MDV is configured to store a canonical copy of meta-data,including access control lists (ACLs) and directories, associated withall files stored on the SVS, whereas each DV is configured to store, atleast, data content of those files. For each file stored on the SVS, onevolume is designated the CAV and, to that end, is configured to store(“cache”) certain, rapidly-changing attribute meta-data associated withthat file to thereby offload access requests that would otherwise bedirected to the MDV. In the illustrative embodiment described herein,determination of the CAV for a file is based on a simple rule: designatethe volume holding the first stripe of content (data) for the file asthe CAV for the file. Not only is this simple rule convenient, but italso provides an optimization for small files. That is, a CAV may beable to perform certain operations without having to communicate withother volumes of the SVS if the file is small enough to fit within thespecified stripe width. Ideally, the first stripes of data for files aredistributed among the DVs of the SVS to thereby facilitate evendistribution of CAV designations among the volumes of the SVS. In analternate embodiment, data for files is striped across the MDV and theDVs.

FIG. 14 is a schematic block diagram of the inode files of an SVS 1400in accordance with an embodiment of the present invention. The SVS 1400illustratively comprises three volumes, namely MDV 1405 and two DVs1410, 1415. It should be noted that in alternate embodiments additionaland/or differing numbers of volumes may be utilized in accordance withthe present invention. Illustratively, the MDV 1405 stores a pluralityof inodes, including a root directory (RD) inode 1420, a directory (DIR)inode 1430, file (F) inodes 1425, 1435, 1445 and an ACL inode 1440. Eachof these inodes illustratively includes meta-data (M) associated withthe inode. In the illustrative embodiment, each inode on the MDV 1405does not include data (D); however, in alternate embodiments, the MDVmay include user data.

In contrast, each DV 1410, 1415 stores only file (F) inodes 1425, 1435,1445 and ACL inode 1440. According to the inventive architecture, a DVdoes not store directories or other device inodes/constructs, such assymbolic links; however, each DV does store F inodes, and may storecached copies of ACL inodes, that are arranged in the same locations astheir respective inodes in the MDV 1405. A particular DV may not store acopy of an inode until an I/O request for the data container associatedwith the inode is received by the D-Module serving a particular DV.Moreover, the contents of the files denoted by these F inodes areperiodically sparse according to SVS striping rules, as describedfurther herein. In addition, since one volume is designated the CAV foreach file stored on the SVS 1400, DV 1415 is designated the CAV for thefile represented by inode 1425 and DV 1410 is the CAV for the filesidentified by inodes 1435, 1445. Accordingly, these CAVs cache certain,rapidly-changing attribute meta-data (M) associated with those filessuch as, e.g., file size 615, as well as access and/or modification timestamps 620.

According to another aspect of the invention, the SVS is associated witha set of striping rules that define a stripe algorithm, a stripe widthand an ordered list of volumes within the SVS. The striping rules foreach SVS are illustratively stored as an entry of VLDB 1130 and accessedby SVS ID. FIG. 15 is a schematic block diagram of an exemplary VLDB SVSentry 1500 in accordance with an embodiment of the present invention.The VLDB entry 1500 includes a SVS ID field 1505 and one or more sets ofstriping rules 1530. In alternate embodiments additional fields 1535 maybe included. The SVS ID field 1505 contains the ID of a SVS which, inoperation, is specified in data container handle 500.

Each set of striping rules 1530 illustratively includes a stripe widthfield 1510, a stripe algorithm ID field 1515, an ordered list of volumesfield 1520 and, in alternate embodiments, additional fields 1525. Thestriping rules 1530 contain information for identifying the organizationof a SVS. For example, the stripe algorithm ID field 1515 identifies astriping algorithm used with the SVS. In the illustrative embodiment,multiple striping algorithms could be used with a SVS; accordingly,stripe algorithm ID is needed to identify which particular algorithm isutilized. Each striping algorithm, in turn, specifies the manner inwhich file content is apportioned as stripes across the plurality ofvolumes of the SVS. The stripe width field 1510 specifies the size/widthof each stripe. The ordered list of volumes field 1520 contains the IDsof the volumes comprising the SVS. In an illustrative embodiment, theordered list of volumes comprises a plurality of tuples comprising of aflexible volume ID and the aggregate ID storing the flexible volume.Moreover, the ordered list of volumes may specify the function andimplementation of the various volumes and striping rules of the SVS. Forexample, the first volume in the ordered list may denote the MDV of theSVS, whereas the ordering of volumes in the list may denote the mannerof implementing a particular striping algorithm, e.g., round-robin.

A Locate( ) function 375 is provided that enables the VSM 370 and othermodules (such as those of N-module 310) to locate a D-module 350 and itsassociated volume of a SVS 1400 in order to service an access request toa file. The Locate( ) function takes as arguments, at least (i) a SVS ID1505, (ii) an offset within the file, (iii) the inode number for thefile and (iv) a set of striping rules 1530, and returns the volume 910on which that offset begins within the SVS 1400. For example, assume adata access request directed to a file is issued by a client 180 andreceived at the N-module 310 of a node 200, where it is parsed throughthe multi-protocol engine 325 to the appropriate protocol server ofN-module 310.

To determine the location of a D-module 350 to which to transmit a CFmessage 400, the N-module 310 may first retrieve a SVS entry 1500 toacquire the striping rules 1530 (and list of volumes 1520) associatedwith the SVS. The N-module 310 then executes the Locate( ) function 375to identify the appropriate volume to which to direct an operation.Thereafter, the N-Module may retrieve the appropriate VLDB volume entry1200 to identify the aggregate containing the volume and the appropriateVLDB aggregate entry 1300 to ultimately identify the appropriateD-module 350. The protocol server of N-module 310 then transmits the CFmessage 400 to the D-module 350.

H. Sparse Files

The present invention provides a storage system architecture comprisingone or more volumes distributed across a plurality of nodesinterconnected as a cluster. The volumes are organized as a SVS andconfigured to store content of data containers, such as files andlogical units, served by the cluster in response to multi-protocol dataaccess requests issued by clients. Each node of the cluster includes (i)a storage server adapted to service a volume of the SVS and (ii) amulti-protocol engine adapted to redirect the data access requests toany storage server of the cluster. Notably, the content of each datacontainer is apportioned among the volumes of the SVS to thereby improvethe efficiency of storage service provided by the cluster.

As noted, the SVS is associated with a set of striping rules that definea stripe algorithm, a stripe width and an ordered list of volumes withinthe SVS. The stripe algorithm specifies the manner in which datacontainer content is apportioned as stripes across the plurality ofvolumes, while the stripe width specifies the size/width of each stripe.Moreover, the ordered list of volumes may specify the function andimplementation of the various volumes and striping rules of the SVS. Forexample, the ordering of volumes in the list may denote the manner ofimplementing a particular striping algorithm, e.g., round-robin.

According to an aspect of the invention, each data container storedwithin a SVS is implemented as a sparse data container. Each datacontainer stored within the SVS comprises one or more stripes of datastored on each constituent volume of the SVS in accordance with thestripe algorithm associated with the SVS. A region of each constituentvolume that is not currently storing a stripe of data is implemented asa sparse region with no assigned back-end storage. By utilizing regionsof sparseness, each data stripe of a data container within a SVS islocated at a predetermined offset. Illustratively, the predeterminedoffset is equal to the stripe number minus 1 multiplied by the stripesize, as the first stripe is located at offset zero, e.g., the fifthstripe of data begins at an offset four times the stripe width.

Advantageously, the use of sparse data containers facilitates processingof re-striping operations by moving a stripe of data from a currentlocation on a volume to an intended offset (destination) of anappropriate destination volume. The destination is thus sparse at thedestination volume, thereby enabling easy re-striping operations.Additionally, if metadata associated with the SVS is damaged to anextent that it is impossible to identify the striping algorithm, thedata container may be efficiently reconstructed by examining each of theconstituent volumes of the SVS and noting that the first stripe of datais located at offset zero, the second stripe of data located at anoffset equal to the striped width, etc. Thus, the use of sparse datacontainers also improves data availability and protection.

FIG. 16 is a schematic block diagram illustrating the periodicsparseness of file content stored on volumes A 1605, B 1610 and C 1615of SVS 1600 in accordance with an embodiment of the present invention.As noted, file content is periodically sparse according to the SVSstriping rules, which specify a stripe algorithm (as indicated by stripealgorithm ID field 1515) and a size/width of each stripe (as indicatedby stripe width field 1510). Note that, in the illustrative embodiment,a stripe width is selected to ensure that each stripe may accommodatethe actual data (e.g., stored in data blocks 806) referenced by a singleindirect block (e.g., level 1 block 804) of a file.

In accordance with an illustrative round robin striping algorithm,volume A 1605 contains a stripe of file content or data (D1) 1620followed, in sequence, by two stripes of sparseness (S) 1622, 1624,another stripe of data (D4) 1626 and two stripes of sparseness (S) 1628,1630. Volume B 1610, on the other hand, contains a stripe of sparseness(S) 1632 followed, in sequence, by a stripe of data (D2) 1634, twostripes of sparseness (S) 1636, 1638, another stripe of data (D5) 1640and a stripe of sparseness (S) 1642. Volume C 1615 continues the roundrobin striping pattern and, to that end, contains two stripes ofsparseness (S) 1644, 1646 followed, in sequence, by a stripe of data(D3) 1648, two stripes of sparseness (S) 1650, 1652 and another stripeof data (D6) 1654. By utilizing the sparse file implementation of thepresent invention, each strip of data is located at the appropriateoffset within the SVS, i.e. D1 located in the first stripe, D2 at thesecond, etc.

FIG. 17 is a schematic block diagram of an exemplary inode buffer tree1700 showing periodic sparseness of a file in accordance with anembodiment of the present invention. The inode buffer tree 1700 includesan inode 1705 having a plurality of pointers (“data” pointers) 1710,each of which points to (references) one or more indirect blocks 1715.Although the data pointers of inode 1705 illustratively reference level1 indirect blocks 1715, in alternate embodiments of the presentinvention, those pointers may reference differing levels of indirectblocks and/or directly reference level 0 data blocks. As such, thedescription of inode 1705 referencing level 1 blocks 1715 should betaken as an exemplary only. Each indirect block 1715 contains aplurality of pointers, either data pointers 1720 that point to level 0data blocks 1730 or “sparse” pointers 1725, which represent regions ofsparseness exemplified by sparse level 0 blocks 1735. As such, sparselevel 0 data blocks 1735 are not physically stored within the filesystem and are shown for illustrative purposes only. It should be notedthat in the illustrative embodiment, each sparse pointer 1725 embodies aspecial value signifying that the pointer is a sparse pointer. Dependingon the size of the sparse regions, one or more indirect blocks 1715 maybe composed entirely of sparse pointers.

FIG. 18 is a schematic block diagram illustrating reconstruction of afile having periodic sparseness in accordance with an embodiment of thepresent invention. Illustratively, the file is the same as file 1600discussed above in reference to FIG. 16. Each stripe of data of a sparsefile is stored at an appropriate offset within a volume of a SVS,thereby enabling easy reconstruction of the file should metadataassociated with striping rules, etc. be lost and/or damaged. Forexample, reconstructed file 1805 includes data stripe D1 1620 at a firstoffset, data stripe D2 1634 at a second offset, data stripe D3 1648 atthe third offset, data stripe D4 1626 at the fourth offset, data stripeD5 1640 at the fifth offset and data stripe D6 1654 at the sixth offset.Should metadata relating to the striping algorithm be lost/damaged, thefile system may reconstruct the file by scanning the first offset withineach volume until it locates a non-sparse region. This process may berepeated for each following offset until the file is completelyreconstructed.

FIG. 19 is a flowchart detailing the steps of a procedure 1900 forcreating and using a SVS with sparse files in accordance with anembodiment of the present invention. The procedure 1900 begins in step1905 and continues to step 1910 where an administrator defines a SVS bycreating a set of striping rules. This may be performed, e.g., by usingoperations available via the management framework 1110. As noted above,a SVS is defined by a set of striping rules 1500. In response todefining the set of striping rules, the storage system then, in step1915, organizes a plurality of volumes as the SVS. The volumes that areorganized are those volumes defined within the list of volumes field1520 of the striping rules 1500. Once the SVS has been defined and theappropriate volumes organized as the SVS, the storage system may thenstore file(s) within the SVS as sparse data containers among each of theplurality of volumes in step 1920. Such storage is illustratively inaccordance with the striping algorithm identified by the set of stripingrules. The procedure then completes in step 1925. It should be notedthat various operations, e.g., reads, write, etc. may be performed. Suchoperations are further described in the above-incorporated U.S. patentapplication Ser. No. 11/119,278, which was filed on Apr. 29, 2005, byMichael Kazar, et al. and entitled STORAGE SYSTEM ARCHITECTURE FORSTRIPING DATA CONTAINER CONTENT ACROSS VOLUMES OF A CLUSTER, nowpublished as U.S. Patent Application Publication No. 2005/0192932 onSep. 1, 2005.

The use of sparse data containers according to the present inventionovercomes several disadvantages associated with the use of dense datacontainers in a SVS. Specifically, stripes of data are stored at easilydiscernable offsets within the data containers so that in the event thatmetadata relating to the stripe algorithm is lost and/or damaged, thedata container may be efficiently reconstructed. Additionally, duringre-striping operations, a stripe that is moved may be copied to its newlocation and stored in the previously sparse region of the datacontainer. Furthermore, the sparseness of a data container may beexploited when performing certain operations, including writing datathat extends beyond a single stripe. Such uses are described in U.S.patent application Ser. No. 11/119,279, entitled for SYSTEM AND METHODFOR IMPLEMENTING ATOMIC CROSS-STRIPE WRITE OPERATIONS IN A STRIPEDVOLUME SET, by Richard P. Jernigan, IV, et al.

The foregoing description has been directed to particular embodiments ofthis invention. It will be apparent, however, that other variations andmodifications may be made to the described embodiments, with theattainment of some or all of their advantages. Specifically, it shouldbe noted that the principles of the present invention may be implementedin non-distributed file systems. Furthermore, while this description hasbeen written in terms of N and D-modules, the teachings of the presentinvention are equally suitable to systems where the functionality of theN and D-modules are implemented in a single system. Alternately, thefunctions of the N and D-modules may be distributed among any number ofseparate systems, wherein each system performs one or more of thefunctions. Additionally, the procedures, processes and/or modulesdescribed herein may, be implemented in hardware, software, embodied asa computer-readable medium having program instructions, firmware, or acombination thereof. Therefore, it is the object of the appended claimsto cover all such variations and modifications as come within the truespirit and scope of the invention.

1. A system, comprising: two or more computers coupled together to forma cluster; a plurality of volumes distributed across the two or morecomputers to form a striped volume set, wherein the striped volume setis defined by a set of striping rules, and each volume is a logicalarrangement of a plurality of storage devices attached to a computer ofthe two or more computers; a volume striping module configured toexecute on one or more computers in the cluster, wherein the volumestriping module stripes one or more data containers across the stripedvolume set; and a plurality of data containers stored across the stripedvolume set, wherein each data container stores one or more stripes ofdata on each volume and is configured with one or more sparse regions,wherein the one or more sparse regions are used to maintain that eachstripe of data is stored at a predetermined offset, wherein the set ofstriping rules comprises a stripe width and wherein the predeterminedoffset is equal to a stripe number minus 1 multiplied by the stripewidth.
 2. The system of claim 1, wherein the plurality of volumes is aplurality of virtual volumes.
 3. The system of claim 2, wherein one ormore storage devices of the plurality of storage devices attached to thecomputer of the two or more computers are logically arranged to form anaggregate with a global storage space.
 4. The system of 3, wherein oneor more of the plurality of virtual volumes are stored within theaggregate of the computer.
 5. The system of claim 1, wherein theplurality of volumes are physical volumes.
 6. The system of claim 1,wherein the data container is a file or a lun.
 7. The system of claims1, wherein one volume of the plurality of volumes is a metadata volumeconfigured to store access control lists and directories of at least onedata containers stored across the striped volume set.
 8. The system ofclaim 7, wherein one or more volumes of the plurality of volumes is adata volume and stores data of the at least one data container.
 9. Thesystem of claim 1, wherein the set of striping rules comprises astriping algorithm identifier that identifies a striping algorithmutilized with the striped volume set.
 10. The system of claim 1, whereinthe set of striping rules comprises an ordered set of volumes.
 11. Amethod, comprising: coupling two or more computers together to form acluster; organizing a plurality of volumes as a striped volume set usinga set of striping rules, wherein the plurality of volumes aredistributed across the cluster and each volume is a logical arrangementof a plurality of storage devices attached to a computer of the two ormore computers; and storing a plurality of data containers across thestriped volume set, wherein each data container stores one or morestripes of data on each volume and is configured with one or more sparseregions, wherein the one or more sparse regions are used to maintainthat each stripe of data is stored at a predetermined offset, whereinthe set of striping rules comprises a stripe width and wherein thepredetermined offset is equal to a stripe number minus 1 multiplied bythe stripe width.
 12. The method of claim 11, wherein the set ofstriping rules comprise an ordered set of volumes.
 13. The method ofclaim 11, wherein the set of striping rules comprise a stripingalgorithm identifier that identifies a striping algorithm utilized withthe striped volume set.
 14. The method of claim 11, wherein the datacontainer is a file or a lun.
 15. The method of claims 11, wherein atleast one volume of the plurality of volumes is a metadata volumestoring access control lists and directories of at least one datacontainer stored across the striped volume set, and wherein one or morevolumes of the plurality of volumes is a data volume storing data of theat least one data container.
 16. The method of claim 11, wherein theplurality of volumes is a plurality of virtual volumes.
 17. The methodof claim 11, wherein one or more storage devices of the plurality ofstorage devices attached to the computer of the two or more computersare logically arranged to form an aggregate with a global storage space,and storing, at the aggregate, one or more virtual volumes of theplurality of virtual volumes.
 18. The method of claim 11, wherein theplurality of volumes are physical volumes.